In a material handling vehicle, it is conventional for the vehicle to be provided with a multi-part arm where each part of the arm is movable relative either to the vehicle or other parts of the arm by a suitable actuator, conventionally a fluid-operated ram. It is generally the case that each actuator is controlled separately by an operator by operation of an associated valve or control. In general, at least one of the actuators causes pivotal movement of a arm part relative either to the structure of the vehicle itself or to another part of the ann. Consequently, where it is required to move a material handling implement mounted on the arm along a desired path, and in particularly in a generally straight line, a great deal of skill is required on the part of an operator to provide the relative movement between the arm parts and the vehicle such that the material handling implement moves along the desired path. A particular example is in backhoes. Backhoes have at least two arm parts, one of which is pivotally mounted on the vehicle structure and the other arm part which is pivotally mounted on the first arm part In applications such as digging an excavation. it is desirable to move a material handling implement in the form of a bucket provided on the arm in a straight line towards the vehicle to provide an appropriate flat bottom trench, and a great deal of operator skill is required to cause the requisite pivotal movement of the arm parts to cause the bucket to move along its desired path
A source of difficulty for the operator is that the operator has to judge by eye the three-dimensional position of the material handling implement arid operate the controls accordingly to move the material handling implement along a desired path. In the example, of a backhoe, the material handling implement may be hidden from the operator's view by the arm, and where the backhoe is being used for an excavation, the base of the trench may also be partly hidden from the driver. It is known to provide a camera on the arm and a television monitor in the cab to enable the operator to, for example, look at the ground underneath the material handling implement to be able to check for obstructions such as buried pipes but this is only of limited assistance in judging the position of the material handling implement and requires the operator to look at a screen and away from the material handling implement itself.